The present invention relates to a device and method for conducting geotechnical and geoenvironmental measurements using direct push tools, and more particularly to a latching and retrieval system that allows the in situ interchange of several different tools including, but not exclusively, an electric cone penetrometer, a soil core sampler, a soil vapor sampler, and a grouting device, all through an embedded direct push rod string without requiring withdrawal of the string. The device also allows the collection and retrieval of soil core samples from multiple depths during a single penetration without requiring withdrawal of the rod string.
Currently, the use of multiple direct push tools during a site characterization (i.e., piezocone, chemical sensors, core sampler, grouting tool) must be accomplished by withdrawing the entire penetrometer rod string to change tools. This practice results in multiple penetrations being required during characterization of a site, and to subsequently seal the resulting multitude of holes with grout.
The present invention allows multiple tools to be interchanged during a single penetration without withdrawing the rod string from the ground. This allows more work to be accomplished and reduces overall costs as time is not wasted pulling rods back out of the ground to change tools or retrieve soil core samples.
The implementation of a wireline tool approach to direct push technologies is unique from drilling implementations because in contrast to drilling (1) direct push incorporates direct sensing tools at the tip of the rod string, (2) direct push relies entirely on the transmission of axial force through instruments at the tip of the rod string to penetrate the earth, and (3) direct push tools are used to measure in situ stresses, electrical properties, the presence of chemical, and other properties as a means of characterization. Because of these differences direct push uses smaller diameter casings than drilling, with relatively greater wall thickness, and requires the accommodation of electrical cabling and/or optical fibers within the rod string.
The wireline system for multiple direct push tool usage of the present invention is composed of several components which are similar in function to conventional direct push and cone penetrometer technology (CPT) equipment used for in situ geoenvironmental. site characterization. Conventional equipment uses either a heavyweight push truck to advance tools into the earth under static load (cone penetration testing), or a percussion hammer approach using a lighter rig. The electronic probes are instrumented and signals are transmitted to the surface via electrical cable and/or fiber optics strung through the center of the hollow push rods. Also typical is the simple collection of multiple soil core samples.
With the wireline system of the present invention, the same method is used to advance the rod string into the earth. However, in the present invention, the first rod (i.e., the deepest one) has a provision for a latching mechanism that allows various tools to be locked into and unlocked from the rod string, as well as retrieved and deployed through the rod string while the rod string remains embedded in the ground. This system allows instrumented probes and samplers, as well as other tools, to be used during a single penetration.
The wireline system consists of six major components:
rods,
latching mechanism,
soil core sampler,
piezocone module,
vapor sampler, and
grout module.
Rods: The push rods have a relative wall thickness (about 19% of the diameter) exceeding that a typical drive casings used with drilling technologies because direct push systems do not rely on rotary action, cutting bits, or augers to remove material from the path of the rod string, and thus must support the transmission of greater axial load relative to casing diameter than drilling systems in order to penetrate the earth. Typical direct push rod diameters range from about one inch to two and a quarter inches.
The wireline rod string of the present invention has a two-inch outer diameter and a one and one-quarter inch inner diameter. The shouldered joints of the one-meter rod segments are joined by double-lead rope threads which connect faster and sustain greater loading than V-threads.
The rod string optionally incorporates occasional rod expanders (one on every fifth or sixth rod in the string). Expanders are rings welded to the outside of the rods which widen the borehole beyond the normal outside diameter of the rod segments as they pass into the earth, thus creating an annular void between the earth and the normal outer rod surface which alleviates sidewall friction that can accumulate along the embedded length of the rod string. By this action, the expanders enable deeper penetration in some soils than would be achievable without them when using the system.
Latching Mechanism: The latching mechanism comprises two main components, one stationary and the other removable. The stationary component is also the lowermost push rod segment. It is a specialized segment called the tool housing which embodies the receiving mechanism for the removable element. The removable element is the lock assembly.
The lock assembly employs two horizontally opposed, hinged locking dogs which lock the tools into place by rotating outward to occupy a receiving groove in the inside surface of the tool housing. The dogs are held in the locked position by a locking wedge which slides vertically between them. This dog arrangement allows the axial stress on the direct push tools from application of static force, rapid percussion, or other dynamic loading to be distributed over a greater bearing area than on systems used in conventional drilling.
This fulfills the unique requirement of the direct push application for more bearing capacity than required in wireline drilling arrangements because direct push tools encounter the stress of penetration, which must be transferred to the rod string, whereas with drilling, less axial stress is generated on the tools and the outer casing carries most of the bearing load directly. When the locking dogs are in the engaged position, a spring-loaded locking wedge rests between them, preventing retraction of the dogs.
A retraction system allows disengagement of the locking dogs in the latching mechanism by displacement of a spring-loaded locking wedge which travels vertically between the dogs and has a conic outer surface at its base, a cylindrical outer surface above the conic surface, and a smaller diameter shaft above that. The dogs have a vertical inner surface that is beveled at the top, such that when the dogs are not engaged, the wedge must be in a raised position with its conic surface acting against the complementary beveled surface on the dogs, but when the dogs are engaged, the wedge is in a lower position with its vertical surface acting against a vertical surface on the interior of the dogs.
The nature of the contact between the wedge and the dogs disallows retraction of the dogs when the vertical surfaces are in contact, regardless of the inward force exerted on the dogs by the receiving groove, but allows the dogs to retract in response to inward force when the wedge has been raised enough that the conic surfaces are in contact. When not counteracted for retrieval, a compression spring around the shaft of the locking wedge keeps the wedge in the downward position.
The lock mechanism allows the deployed tool to lock into place upon reaching an appropriate depth. A landing nut allows free fall deployment of tools, fine tuning of lock clearances, and easy replacement of the most wear-receiving parts.
The tool housing is a specialized version of the individual rods segments that compose the rod string. First, it is shorter than the one-meter length of the other rods. Second, while the inner diameter of most of the tool housing is identical to that of the individual rods in the string, the tool housing adds a receiving groove of wider diameter than the rod inner diameter, and an interior threaded section which holds the landing nut of lesser inner diameter than the rods.
In the retracted position, the outer surface of the dogs is contained within a smaller diameter than the interior of the rods, but larger than the inner diameter of the landing nut, so the landing nut stops the dogs from overshooting the receiving groove and keeps tools from overextending beyond the bottom of the rod string. The nut also provides the ability to adjust the receiving groove size so that the fit of the locking dogs can be fine-tuned. The system is designed such that the nut receives the impact of falling tools, and is easily replaced if wear becomes an issue.
A compression spring surrounds the shaft of the locking wedge. This spring causes the locking wedge to exert an outward force on the locking dogs whenever they are partially or fully retracted. This outward force has several advantages. First, it causes instant extension of the dogs into the engaged position when the receiving groove in the tool housing is encountered. Second, it keeps tools centered in the rod string as they are lowered down to the tip for deployment. There is always an outward component of force on the locking dogs, whenever they are not fully extended and the retrieval wire is free of tension.
The chamfered lower edge of the locking dogs allows them to skate over discontinuities and imperfections in the interior rod surface, such as where joints occur in the rod string. The action of the dogs as they skate down the interior surface of the rods also results in cleaning of the surface,.by scraping impurities from the surface and allowing them to drop out the open bottom of the rod string.
Finally, once the dogs are engaged in the receiving groove, the spring-loading of the locking wedge prevents vertical displacement of the wedge from between the locking dogs that would allow the dogs to retract and disengage under the rod acceleration induced by vibratory or percussion driving. The wedge also has a hole through the center to allow the pass-through of electrical wiring, a grout tube, or optical fibers to the tools below.
Tools are retrieved by pulling up a retrieval wire attached to the locking wedge by a connector block. This removes the locking wedge from between the dogs and allows the dogs to retract under the load of the tool pushing the dogs against the upper, beveled surface of the receiving groove. Tools are redeployed by lowering them down the rod string using the retrieval cable until they come to rest against the landing nut, and the dogs snap into place in the tool housing.
Piezocone: The piezocone tool incorporates standard gauges for tip stress, sleeve stress and pore pressure. The system is designed such that the piezocone can be lowered down the rod interior and locked into place. Once locked in place the piezocone and the rod can be advanced together.
The system is capable of unlocking the probe at any depth for installation of either a dummy tip, another probe, or the grouting tool. The wireline piezocone tool is 1.125 inches in diameter. This diameter corresponds to a 6.5 cm2 projected cone area.
The piezocone maintains appropriate ratios of sleeve area to tip area. The probe mandrel and probe body are sized relative to each other such that if sufficient bending stress to break the tool were developed in the subsurface during deployment, the probe would fail at the mandrel rather than at the body, thus minimizing the potential for damage to other wireline system components.
Soil Sampler: The soil sampler tool allows the collection and retrieval of core samples from multiple depths during a penetration without requiring retraction of the CPT rods from the ground. The sample barrel produces a one-inch diameter, 12-inch long core of soil, accommodates the use of a plastic retainer basket (for loose soils), and is easily separable from the locking mechanisms and basket retainer nut. Either end of the barrel connects to these other parts, or to end plugs used for sealing the sample. The nut used to hold in the retainer basket receives the tip soil stress and prevents wear or damage to the leading edge of the core barrel.
Grouting Module: The system includes a grouting module to permit grouting a penetration upon retraction of the rod string, such that the entire void created by the penetration process is filled with grout. The tool allows the grout to flow from the down-hole end of the rod string during retraction to ensure that the entire void created by the penetration process is filled with grout. This approach to grouting meets the regulatory guidelines of most Environmental Protection Agency (EPA) regional offices.
Tubing is used to transport the grout from the pump to the grouting tool at the end of the rod string. The grouting tool locks in place at the end of the down-hole end of the push rods and is interchangeable with the piezocone and other tools.
Prior to the present invention, the use of multiple characterization tools at a single location during a direct push investigation required typically at least 100% (1xc3x97) re-penetration (for grouting) and as much as 2000% (20xc3x97) re-penetration (for collecting continuous soil core samples).
The manner in which the invention allows multiple tools to be used in a single penetration and allows the retrieval of several soil core samples during a single penetration without withdrawing the rods results in a remarkable time savings for continuous sampling activities. In most cases, it will completely eliminate the incidence of re-penetration. Data from field demonstrations of the invention have indicated time savings of up to 75% for a typical characterization. Once the penetration has begun, a typical one-foot direct push wireline soil sample can be collected every two to three minutes, whereas conventional direct push soil sampling averages about 10 to 15 minutes per foot.
Additionally, it is a requirement of some environmental regulators that the borehole created by a CPT sounding or collection of samples in a contaminated area be sealed with grout upon retraction of the borehole casing. This has prohibited the application of direct push technology in some areas, whereas the present invention allows grouting upon retraction by exchange of the characterization tools with the grouting tool. The ability to place grout in the same hole upon withdrawal also eliminates the possibility of creating a new hole when a hole has to be repenetrated to complete a grouting operation.
Although the use of wireline tools in conjunction with drilling for subsurface characterization has been well established, applying wireline concepts to direct push technology is novel and unique from drilling implementations. In contrast to drilling, direct push technology (1) usually incorporates direct sensing tools at the tip of the rod string, (2) subjects the tools at the tip of the rod string to greater axial force that must be transferred to the rod string, in order to penetrate the earth, and (3) direct push tools are used to measure in situ stresses, electrical properties, the presence of chemical, and other properties as a means of characterization during penetration. Because of these differences direct push typically uses smaller diameter casings than drilling, with relatively greater wall thickness, and requires the accommodation of electrical cabling and/or optical fibers within the rod string. The use of semicircular locking dogs, to evenly distribute around the circumference of the rod the load transferred between the tools and the rod string, while allowing a hollow center for passing cables through is a unique advantage.
Another advantage of the latch design of a locking dog geometry is that it transforms axial load on the dogs to a radial compression load on the locking wedge. This removes load from the hinge pins and averts the need for parts with large cross-sectional areas to resist shear loads.
Because direct push technology is relatively new and offers many significant advantages over drilling for environmental characterization even without the use of wireline tools, few practitioners of the direct push technology recognize the potential for time saving and cost saving afforded by this approach.
Direct push systems incorporate rods that are relatively small diameter relative to drilling tools. Due to the size constraints of conducting mechanical latching operations inside a direct push rod, how to successfully develop a wireline system for multiple direct push tool usage has not been readily apparent to practitioners in the art.
Accordingly, it is an object of the present invention to use a direct push rod string for the measurement of soil parameters through the use of a series of replaceable measurement modules which are lowered through the rod string and locked in a tool housing in a leading end of the rod string and which can be released from the tool housing and withdrawn through the rod string for replacement with a different soil measuring module.
It is another object of the present invention to use a direct push rod string for the measurement of soil parameters through the use of a series of replaceable measurement modules which are lowered through the rod string and locked in a tool housing in a leading end of the rod string and which can be released from the tool housing and withdrawn through the rod string for replacement with a different soil measuring module by the use of a latching mechanism for securing the measurement module in the tool housing by two opposed locking dogs engaged by a locking wedge to force the dogs into a receiving groove on the interior surface of the tool housing and biasing the locking wedge for forcible retraction of the locking wedge by a wireline and allowing retraction of the dogs from the receiving groove for withdrawal of the measurement module or probe.
It is still yet another object of the present invention to use a direct push rod string for the measurement of soil parameters through the use of a series of replaceable measurement modules which are lowered through the rod string and locked in a tool housing in a leading end of the rod string and which can be released from the tool housing and withdrawn through the rod string for replacement with a different soil measuring module by the use of a latching mechanism for securing the measurement module in the tool housing by two opposed locking dogs engaged by a locking wedge to force the dogs into a receiving groove on the interior surface of the tool housing and biasing the locking wedge for retraction of the locking wedge by a wireline and allowing retraction of the dogs from the receiving groove for withdrawal of the measurement module with the locking dogs being chamfered on a lower edge to allow the dogs to skate over discontinuities in the rod string and having a chamfered upper edge to assist in retraction of the dogs from the receiving groove upon release of the dogs by the locking wedge.